We were musing here about how common it is to want more than two Y axes on a plot. Checking out the File Exchange, there seem to be several candidates, indicating that this is something at least some people find useful.
Here's a sample plot using plotyy that comes with MATLAB.
x = 0:0.01:20; y1 = 200*exp(-0.05*x).*sin(x); y2 = 0.8*exp(-0.5*x).*sin(10*x); plotyy(x,y1,x,y2,'plot');
In addition to plotyy in MATLAB, here's a list of some of the candidates from the File Exchange.
I am curious to know what kind of data or results you are plotting so that having multiple y-axes makes a compelling presentation. Let us know here.